Piston and fire ring construction



March 1965 D. M. HESLING ETAL 3,

PISTON AND FIRE RING CONSTRUCTION Filed Jan. 29, 1962 2 Sheets-Sheet 1F15. s Fm. 4

WENTORS DONALD M. HESLING, LAVERNE KIBBEY 6; LEWIS M. DAvls ATTORNEYSMarCh 1965 D. M. HESLING ETAL 3,174,762

PISTON AND FIRE RING CQNSTRUCTIDN Filed Jan. 29, 1962 2 Sheets-Sheet 2 I1 TORS 44 DONALD M. HESLING, LAVERIWE MFYIBBEY 6c LEWIS M. DAV/5,

A a. M

ATTORNEYS United States Patent 3,174,762 PISTGN AND FREE RHNGfIQNSTRUfITlGN Donald M. Heeling, Laverne W. Kibbey, and Lewis M.

Davis, Muskegon, Mich, assignors to Sealed Power Corporation, Muskegon,Mich, a corporation of Michigan Filed Jan. 29, N62, Ser. No. 169,514Claims. (Cl. 277-193) This invention relates to a piston and fire ringconstruction for use in internal combustion engines, particularly dieselengines.

Sticking of the top compression ring and bore scuffing have beenproblems in diesel engines, particularly in engines which have beenmodified, run at higher speeds or turbocharged in order to increase thehorsepower output of the engines.

The piston configuration and piston ring arrangement normally used inthese heavy duty engines is such that the top compression ring is placeda considerable distance from the top surface of the piston, leaving anunusually wide head land. This is especially true in open chamber typediesels where part or all of the combustion chamber is in the head ofthe piston. The large mass of metal in the head land in the top ringgroove area becomes very hot since it is exposed to the flame of thecombustion process. However, fuel and lubricating oil are only partiallyburned in tins area and consequently a hard deposit forms. Bore scutfingcan result when the deposit on the head land becomes sufficiently thickto take up the normal clearance provided between the land and thecylinder wall. Scufiing can also occur when carbon deposits frompartially-burned fuel and lubricating oil fill up the normal clearancebetween the inside diameter of the top compression ring and the rootdiameter of the piston groove, or between the side of the ring and theside of the groove. In both of the latter cases, when the ring operatingclearances are taken up the outside diameter of the ring is permanentlyexposed beyond the piston lands. Therefore, when the piston rocksslightly during its normal operation, a very high pressure conditionwill exit between the ring face and the cylinder bore and hence scuifingwill result.

An object of the present invention is to provide an improved piston andfire ring assembly for protecting the head land of the piston as well asthe top compression ring thereof located at the conventional position onthe piston.

Another object is to provide an improved fire ring and piston assemblyoperative to shield or bafile the area below the fire ring from theflame front without becoming clogged by carbon deposits in the fire ringgroove.

A further object is to provide an improved piston and fire ring assemblyoperative to keep the cylinder wall scraped free of deposits that mightotherwise work their way into the compression ring grooves located belowthe fire ring groove.

In the accompanying drawing:

FIG. 1 is a fragmentary vertical section of a piston and ring assemblyin a cylinder with the piston and ring assembly constructed inaccordance with the present invention.

FIG. 2 is a plan view of a fire ring segment of the present invention.

FIG. 3 is a fragmentary enlarged view of a portion of FIG. 1illustrating two fire ring segments assembled in the fire ring groove ofthe piston in accordance with the present invention.

FIG. 4 is a fragmentary sectional view corresponding to that of FIG. 3but reduced in scale therefrom, illustrating a modified piston grooveconstruction for aluminum pistons provided with the present invention.

FIG. 5 is a fragmentary sectional View similar to that of FIG. 4illustrating a still further modified piston groove construction.

amass Patented Mar. 23, 1965 "Ice FIGS. 6 and 7 are fragmentarysectional views similar to that of FIG. 3 but enlarged thereover toillustrate the operation of the piston and fire ring assembly of FIG. 3.

Referring to FIG. 1, the piston and fire ring construction of thepresent invention is shown applied to a conventional heavy duty piston10 mounted for reciprocation in a cylinder 12 of a conventional dieselengine, not otherwise shown. circumferential ring grooves 14, 16 and 18for respectively receiving conventional top and middle compression rings20 and 22 and a conventional oil ring 24. Piston It? is designed foropen chamber type diesel engines and hence a large recess 26 is providedin the head of the piston to form part or all of the combustion chamber.As a result the top compression ring 20 is placed a considerabledistance from the top surface 28 of the piston, leaving an unusuallywide head land 30 indicated by the bracket in FIG. 1.

In accordance with the present invention, a circumferential ring groove32 is provided in head land 30 which preferably is located as close aspossible to the top end surface 28 of piston 14) consistent with thestrength of the land material disposed between groove 32 and top surface23. An improved fire ring assembly 34 is inserted in groove 32 whichpreferably comprises two steel segments 36 and 38 as more clearly shownin FIG. 3.

Fire ring segments 36 and 38 are identical and each comprise an annularring (FIG. 2) with a parting gap 39 and an outer peripheral cylinderscraping surface 40 which may be either plain, chrome plated, or coatedor plated with some other wear resistant substance. The fire ringsegments may be made in a conventional manner by coiling up suitablesteel stock into the circular ring configuration of FIG. 2, heattreating the ring to 800 F. to relieve coiling stress and, if desired,plating the outer periphery of the ring to provide the scraping surface40 and then reheating to relieve plating stress. While two fire ringsegments 36, 38 are preferred, fire ring assembly 34 may comprise amultiplicity of such segments or only one of such segments.

One critical feature of the piston and fire ring assembly of the presentinvention resides in the dimensional relationship of the fire rin'assembly 34 relative to the fire ring groove 32 and to the diameter ofthe bore of cylinder 12. The total axial width of the two fire ringsegments 36, 3S, i.e., the dimension of the segments which is parallelto the axis of the piston, is considerably less than the correspondingaxial width of fire ring groove 32. This provides a relatively greatamount of side or axial clearance, such as that shown in FIG. 3 betweenthe top surface 41 of fire ring segment 36 and the top wall 42 of groove32, as compared to the axial clearance normally specified for aconventional compression ring (usually .002-.004 inch). The width ofgroove 32 is the distance between top wall 42 and bottom wall 44 ofgroove 32. It has been found that the best results are obtained when thetwo fire rings 36, 38 are axially dimensioned to provide a total axialclearance ranging from .003 to .012 inch. The preferred range is from.003 to .006 inch. The other important dimensional characteristic offire ring segments 36, 38 is their outside and inside diameters in thefree or expanded condition thereof, the outside diameter beingsubstantially the same as the inside diameter of the bore of cylinder 12so that these segments when installed in piston it within cylinder 12exert little or no radial force against the cylinder wall. The insidediameter of fire ring segments 36, 38 is greater than the root diameterof piston groove 32 so that the segments do not contact or bottomagainst the back wall 43 of the groove during normal operation of theengine.

It will thus be seen that the fire ring assembly 34 has what normallywould be thought of as a sloppy Piston 10 is provided with suitable litin piston groove 32. However, in accordance with the present inventionfire ring assembly 34 is not intended to provide a 100percent seal as isexpected from a compression ring. Rather, the purpose of these firerings is to battle or shield the area below them from the flame frontand also to keep the cylinder wall scraped free of deposits that mightotherwise Work their way into compression ring grooves 14 and 16.

Theoperation of fire ring segments 36 and 38 is best shown in F168. 6and 7. Due to the axial clearance in the ring groove and the lack ofradial pressure against the wall of cylinder 12, the fire ring segments36 and 38 can rotate and shift axially in groove 32 relative to piston10.

This movement is induced by reciprocation of the piston in the cylinderand results in a cleaning action between the top and bottom walls 42 and44 of groove 32 and the respectively adjacent surfaces of fire ringsegments 36 and 38. Since the fire ring segments do not completely sealcompression, no great pressure is built up behind the segments and theyare not forced out against the cylinder wall with extreme pressures.Preferably, the fire ring segments 36, 38 have a high radial thicknessto axial width ratio, such as about six to one, as compared to the usualratio of about two and one quarter to one for conventional compressionrings, and are relatively lightweight. This tends to reduce ring groovepounding due to inertial forces.

Due to their relatively sloppy fit in groove 32, fire ring segments 36and 38 have room in the groove to dish (movement of the ring segmentfrom a planar to a conical shape) between the inclined positionsillustrated in solid lines respectively in FIGS. 6 and 7. The dishingmovement results from the net combined effect of gas pressure, inertialand momentum forces and friction between the first ring segments 36, 38and the wall of the cylinder during reciprocation of the piston. Forexample, on the intake stroke of a four-cycle engine the ring segments36, 38 assume the upwardly dished position of FlG. 6 The downwardlydished position shown in solid lines in FIG. 7 is a transient conditionat the beginning of the compression stroke. During the remainder of thecompression stroke, the combustion stroke and the exhaust stroke thering segments 36, 38 lieflat against the bottom side 44 of groove 32 asindicated in broken lines in FIG. 7. This dishing movement produces whatmay be termed a windshield wiper action between the fire ring segments36, 38 and the wall of cylinder 12 which assists in sweeping thecylinder wall clean. The dishing movement also causes the mutuallyadjacent surfaces of fire ring segments 36, 38 to move radially relativeto one another, thereby assisting in keeping fire ring assembly 34 cleanso that the'fire segments 36, 38 thereof remain free to move radiallyindependently of one another to insure maximum contact of each fire ringscraping sur-. face 40 with the wall of cylinder 12.

When it is desired to install a fire ring assembly in accordance withthe present invention in a piston made of aluminum, or some otherrelatively soft material, it

is preferred'to use the modified piston groove construetion illustratedin FIGS. 4 and 5. In FIG. 4 an alurnlnum piston 50 is partially shownwhich generally corresponds to piston in configuration and in thelocation of top compression ring 20 and a groove 14 therefor. However, 7

instead of casting or machining a 'firc ring groove directly in thematerial of the piston, an .annularcast iron insert 54 is placed in thepiston mold and the molten aluminum is poured around the insert. A firering groove 56 1s then machined'in the cast iron insert 54 to receivefire :ring assembly 34, it being understood thatthe dimensionalrelationship between the fire ring assembly, insert groove 56 and thebore of cylinder 12 is as specified in the previously describedembodiment. Alternatively, as shown in FIG. 5, the aluminum piston 50may be cast with an even larger cast iron insert 60 therein whichencompasses the location of the compression ring 20 as well as fire ringassembly 34. Both a fire ring groove '62 and a compression ring groove64 are then machined of axial clearances between fire ring assembly 34and groove 32 are intended to apply to a range of piston sizes currentlyemployed in known diesel engines of the heavy duty type. Also, the lowerlimit of the aforementioned axialclearance range is more critical thanthe upper limit. If less than the specified minimum clearanceisprovided, ring sticking will be found to occur as in prior art fire ringconstruction. If more clearance is provided than that specified for theupper limit of said range, the fire ring assembly would still beoperable to serve as a baffle to shield the compression rings therebelowfrom the flame front and thereby reduce sticking, but the excessivesloppiness of such a fit would cause hammering of the fire assembly inthe fire ring groove and result in excessive wear of the ring groove.

By way of example and not by way of limitation, a piston and fire ringconstruction operable in accordance with the invention may beconstructed according to the following specifications:

Maximum individual axial width of firering segments 36, 38 as installedAxial width of groove 32 Cylinder bore diameter Free outside diameter offire ring segments 36, 38

.0310 inch. 0.68O.69 inch. About 4.000 to 5.125 in.

Substantially equal to Individual radial thickness of cylinder borediameter.

fire ring segments 36, 38 .l67.l73 inch after Clearance between insidediplating.

meter of ring 24 and root diameter of piston groove 32 Distance acrossgap 39 at free CD. of fire ring segments Material offire ring segments-.032-.042 inch.

0.25 to .065 inch.

Similar to S.A.E-l070 hardened and tempered reduce carbon deposits onthe head land of'the piston and in the top compression ring groove tothereby enable an internal combustion engine to operate for aconsiderably longer period even at wide open throttle without stickin ofeither the compression of the fire rings. It is to be understood thatthe piston and fire ring construction disclosed herein may also beapplied in accordance with the present invention to diesel enginesother'th-an the open chamber'type as well as to gasoline or gas enginesif the above mentioned problems are being encountered.

We claim:

1. In combination: a piston adapted for'reciprocation in an internalcombustion engine cylinder, said piston having a transverse end surfaceadapted to form a movable said end surface including first and secondgrooves re-' spectively constituting the closest and next closestgrooves to said end surface of said plurality of grooves, and 'a headland bounded by said end surface and said second V groove; a set ofpiston rings individually disposed in all but said first groove of saidplurality of grooves including a parted first compressionring disposedin said second groove having a free state outside diameter greater thanthe diameter of the cylinder whereby said compression ring is adapted tobe radially compressed by the cylinder wall to develop compressionsealing contact therewith; and a parted fire ring disposed in said firstgroove and constituting the sole ring element disposed in said firstgroove, said fire ring being dimensioned axially relative to said firstgroove to provide a predetermined axial clearance therebetweensufiicient to permit said fire ring to dish and move axially in saidfirst groove in response to piston reciprocation in the cylinder, saidfire ring having a free state inside diameter greater than the rootdiameter of said first groove to permit rotation of said fire ringrelative to the piston in response to piston reciprocation and said firering having a free state outside diameter substantially equal to thediameter of the cylinder such that said fire ring has a relatively lowunit pressure contact with the cylinder wall compared to that of saidfirst compression ring whereby said fire ring has a mere wiping ratherthan sealing contact with the cylinder wall.

2. The combination set forth in claim 1 wherein said axial clearancebetween said fire ring and said first groove is greater than the axialclearance provided between said compression ring and said second groove.

3. The combination set forth in claim 1 wherein said axial clearancebetween said fire ring and said first groove falls within a range fromabout .003 to .012 inch.

4. The combination set forth in claim 1 wherein said axial clearancebetween said fire ring and said first groove falls within a range fromabout .003 to .006 inch.

5. In combination: a piston adapted for reciprocation in an internalcombustion engine cylinder, said piston having a transverse end surfaceadapted to form a movabl wall of the cylinder combustion chamber, acylindrical peripheral surface having a plurality of circumferentialgrooves therein spaced axially from one another and from said endsurface including first and second grooves respectively constituting theclosest and next closest grooves to said end surface of said pluralityof grooves, and a head land bounded by said end surface and said secondgroove; a set of piston rings individually disposed in all but saidfirst groove of said plurality of grooves including a parted firstcompression ring disposed in said second groove having a free stateoutside diameter greater than the diameter of the cylinder whereby saidcompression ring is adapted to be radially compressed by the cylinderwall to develop compression sealing contact therewith; and a pluralityof parted fire rings disposed in said first groove and constituting thesole ring elements disposed in said first groove, said fire rings eachbeing dimensioned axially relative to one another and to said firstgroove to provide a predetermined axial clearance between the combinedaxial dimension of said fire rings and the axial dimension of said firstgroove sufi'icient to permit said fire rings to dish and move axially insaid first groove in response to piston reciprocation in the cylinder,said fire rings each having a free state inside diameter greater thanthe root diameter of said first groove to permit rotation of said firerings relative to the piston in response to piston reciprocation, saidfire rings each having a free state outside diameter substantially equalto the diameter of the cylinder such that said fire rings each have arelatively low unit pressure contact with the cylinder wall compared tothat of said first compression ring whereby said fire rings each have amere wiping rather than sealing contact with the cylinder wall.

References Cited by the Examiner UNITED STATES PATENTS 765,033 7/04Myers 277-63 XR 2,118,433 5/38 Goodyear 277193 2,294,519 9/42 Starr277-224 XR 2,938,758 5/60 Phillips 277227 XR FOREIGN PATENTS 456,6185/48 Canada.

119,828 10/63 Sweden.

EDWARD V. BENHAM, Primary Examiner.

WALTER A. SCHEEL, Examiner.

1. IN COMBINATION: A PISTON ADAPTED FOR RECIPROCATION IN AN INTERNALCOMBUSTION ENGINE CYLINDER, SAID PISTON HAVING A TRANSVERSE END SURFACEADAPTED TO FROM A MOVABLE WALL OF THE CYLINDER COMBUSTION CHAMBER, ACYLINDRICAL PERIPHERAL SURFACE HAVING A PLURALITY OF CIRCUMFERENTIALGROOVES THEREIN SPACED AXIALLY FROM ONE ANOTHER AND FROM SAID ENDSURFACE INCLUDING FIRST AND SECOND GROOVES RESPECTIVELY CONSTITUTING THECLOSEST AND NEXT CLOSEST GROOVES TO SAID END SURFACE OF SAID PLURALITYOF GROOVES, AND A HEAD LAND BOUNDED BY SAID END SURFACE AND SAID SECONDGROOVE; A SET OF PISTON RINGS INDIVIDUALLY DISPOSED IN ALL BUT SAIDFIRST GROOVE OF SAID PLURALITY OF GROOVES INCLUDING A PARTED FIRSTCOMPRESSION RING DISPOSED IN SAID SECOND GROOVE HAVING A FREE STATEOUTSIDE DIAMETER GREATER THAN THE DIAMETER OF THE CYLINDER WHEREBY SAIDCOMPRESSION RING IS ADAPTED TO BE RADIALLY COMPRESSED BY THE CYLINDERWALL TO DEVELOP COMPRESSION SEALING CONTACT THEREWITH; AND A PARTED FINERING DISPOSED IN SAID FIRST GROOVE AND CONSITUTING THE SOLE RING ELEMENTDISPOSED IN FIRST GROOVE, SAID FIRE RING BEING DIMENSIONED AXIALLYRELATIVE TO SAID FIRST GROOVE TO PROVIED A PREDETERMINED AXIAL CLEARANCETHEREBETWEEN SUFFICIENT TO PERMIT SAID FIRE RING TO DISH AND MOVEAXIALLY IN SAID FIRST GROOVE IN RESPONSE TO PISTON RECIPROCATION IN THECYLINDER, SAID FIRE RING HAVING A FREE STATE INSIDE DIAMETER GREATERTHAN THE ROOT DIAMETER OF SAID FIRST GROOVE TO PERMIT ROTATION OF SAIDFIRE RING RELATIVE TO THE PISTON IN RESPONSE TO PISTON RECIPROCATION ANDSAID FIRE RING HAVING A FREE STATE OUTSIDE DIAMETER SUBSTANTIALLY EQUALTO THE DIAMETER OF THE CYLINDER SUCH THAT SAID FIRE RING HAS ARELATIVELY LOW UNIT PRESSURE CONTACT WITH THE CYLINDER WALL COMPARED TOTHAT OF SAID FIRST COMPRESSION RING WHEREBY SAID FIRE RING HAS A MEREWIPING RATHER THAN SEALING CONTACT WITH THE CYLINDER WALL.